Studying a star system called Kepler-32, which looks like most of the systems throughout the galaxy, Caltech astronomers say there could be 100 billions planets in the Milky Way alone.

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An extraordinary sight just a couple of decades ago, new exoplanets have become commonplace. To date, the Kepler telescope has scoped out thousands of new worlds: some confirmed, some unconfirmed, some living in their system's "habitable zone," and some seemingly too fried or frigid to support life. But while discovering these far-off orbs might not be the landmark achievement it was in the 1990s, the litany of exoplanets now allows astronomers to extrapolate how many worlds there are in the entire galaxy.

The most recent answer: on the order of 100 billion, or one for every star in the Milky Way. (And if you're wondering what that means for the universe, consider that there are at least 100 billion galaxies out there.)

The tally of our galaxy's worlds comes courtesy of scientists at Caltech who work with Kepler. They studied a particular system called Kepler-32, in which at least five planets orbit an M-dwarf star. M-dwarf stars are smaller and cooler than the sun; Kepler-32 is only half as big, the astronomers say. Yet this star is far more typical of the type that populates the galaxy. Three-quarters of all Milky Way stars fit in this class.

As a result, the number and the characteristics of planets orbiting M-dwarfs can tell astronomers more about the Milky Way at large than they could learn from our own solar system, which appears to be a galactic outlier. The added bonus of Kepler-32 is that it has an edge-on orientation in relation to us. That means the orbital plane of its five planets is lined up so that they pass between us and their star, allowing scientists to find them, confirm their existence, study their makeup, and put together an idea of how this star system formed. (Read their release for more.)

The system also suggests that planets in M-dwarf systems orbit their stars at much closer distances than the planets our our solar system orbit their sun. While earth's circuit around our star keeps us about 93 million miles away, all five Kepler-32 worlds orbit within 10 million miles of their star. However, since the star is so much less intense than the sun, the outermost Kepler-32 planet might lie within the habitable zone. Perhaps a great many of the other 100 billion stars in the galaxy do as well.